Waste petroleum constitutes one of the most pernicious environmental problems that man has imposed on this planet. One of the nastiest forms that it takes is petroleum contamination of solid particles. The solid particles derive from many compositions ranging from siliceous materials (e.g., sands, rocks, and the like), carbonaceous materials, clays and clay containing materials, floccular materials with high iron content typically originating from rust flakes, and the like. Recent oil spillages by tankers on European, Scottish and American coastlines dramatize the magnitude of the problem. Petroleum laden solids generated by other acts exist throughout the world, from Singapore to Bahrain to the United States of America. Whether from spillages on land or sea, waste petroleum or pitch land deposits, black oil residues generated in petroleum storage tanks, natural oil or asphalt deposits, in each instance, the removal of the petroleum contamination from the solids is expensive and heretofore generally ineffectual. The petroleum that deposits on the particulate materials will exhibit a higher viscosity owing to the higher surface area of the particulate and the volatilization from the petroleum deposited of some of the lower boiling components. This means that the petroleum so deposited will exhibit a higher viscosity and a greater degree of stickiness when heated so that thermal treatment of the particles causes them to fuse much like asphalt does in constructing a roadway.
A number of approaches have been tried or suggested for the removal of petroleum from solids. A favored approach involves filtering the contaminated solids to remove petroleum that easily separates followed by incineration of the solids to remove the residual petroleum that filtration does not separate. Filtration is relatively ineffective in separating the petroleum because, in any case, about a third of the petroleum will be retained in the voids between the packed particles. Other techniques for removing the petroleum retained by the solids include centering, decanting or hydra separating the waste petroleum and collecting the petroleum laden solids that represent an isolated product of the process. Then the solids may either be dumped in a landfill or incinerated. Dumping in landfills is prohibited in many areas of the world because of the adverse effects the residual petroleum has on insect and animal life, ground water and underground streams, and the like considerations. Incinerating waste petroleum is not cost effective or environmentally acceptable because of the necessity of dealing with NO.sub.x, SO.sub.x and heavy metal emissions. In particular, the petroleum content of the solids after such treatment, such as by filtration, centrifugation and decantation, can be higher than 4-10 percent of the weight of the solids. At those levels of impurities, the solids are environmentally unsafe for landfills. Consequently, laws exist in many countries prohibiting such landfills.
A number of the processes that are promoted for the treatment of waste petroleum employ a final briquetting technique for accumulating the solids containing a residual petroleum content, into a form suitable for applications. This technique suggests the use of the briquettes as a construction material. This merely slows the environmental problem, not eliminate it. Over time, nature will break down the briquettes and eventually the retained petroleum leaches into the earth.
One of the problems that an engineer faces in cleaning solids to remove petroleum residues has to do with the stickiness of the petroleum under conditions that allow its separation from the surface of the solid. For example, one may solvate the petroleum and wipe it off the surface, but that is time consuming and costly because of the need for repeated treatments of the surface to reduce the petroleum concentrations to acceptable levels. It would also seem feasible to expose the particles to hot gases in a fluid bed. However, such dynamic bed applications are vulnerable to particle aggregation (agglomeration) which serves to drop the aggregated particles out of the bed and out of the fluid treatment. Thus, one would expect that fluidization of a bed of petroleum laden particles by a stream of hot gas would first soften the petroleum coating on the particle to a point that it is capable of sticking to other of the particles in the bed. This sticking would generate agglomerates of the particles with increased mass and they would precipitate from the fluid bed. Once they are removed from the bed, they are no longer treatable by the hot gases fed to the bed. When too much of the bed is agglomerated, the bed crashes and fluidization ceases. The agglomerated particles are more difficult to treat than their relatively smaller sized progenitor particles.
There is a need for processes that will effectively remove petroleum from solids so that the solids can be safely deposited in landfills without fear of pollution of underground water or creating other types of environmental problems. The process of this application achieves this by the separation of the residual petroleum in the solids in a useful fuel form or as a feed stock in a operation. A feature of the invention is the treatment of such contaminated solids in a toroidal dynamic bed such as achieved in the apparatus described in Dodson, U.S. Pat. No. 4,479,920, patented Oct. 30, 1984. For unexplainable reasons, the petroleum particles treated in a toroidal dynamic bed are not subject to the kind of agglomeration obtainable in a fluid bed. The technology embodied in the patent, commercially called the "Torbed Process," is being licensed by Davy McKee (London) Limited, London, U.K. The Torbed.RTM. Process is recommended (Gtoszek, "The Torbed Process: A Novel Concept in Heat and Mass Transfer," International Deep Mining Conference: Innovations in Metallurgical Plant, Johannesburg, SAIMM, 1990 and product brochure) for a number of applications, including:
The calcination of clays and lime, magnesite and dolomites to yield both `dead-burnt` and highly reactive products; PA1 The combustion of low calorific value/high ash content fuels in which the carbon burnout was in excess of 99%; PA1 The production of lightweight aggregates through the firing and `bloating` of clays; PA1 Toxic waste incineration; PA1 Regeneration of activated carbons; PA1 Regeneration of catalysts; PA1 Drying of sand, filter cakes, concentrates; PA1 Vaporization; PA1 Gasification; PA1 Pyrolysis; PA1 Heat transfer. PA1 (a) A substantial decoupling of support medium mass flow and `fluidizing` velocity is achieved; PA1 (b) High rates of heat and mass transfer may be realized by utilizing the high impingement velocities of the process gas stream; PA1 (c) The dissipation of the velocity of the support medium provides the means of processing a widely graded material; PA1 (d) Irregular shapes may be processed under strictly controlled conditions; PA1 (e) The low mass and thermal inertia of the bed permits rapid responses to process controls; PA1 (f) There is a low static pressure loss across the toroidal dynamic bed.
The advantages of the Torbed.RTM. Process are alleged to be:
Other patents dealing with the Torbed.RTM. Process include: U.S. Pat. No. 4,559,719; U.S. Pat. No. 4,909,811; U.S. Pat. No. 4,952,140; U.S. Pat. No. 5,033,205; European Patent Public. 0 346 004 and U.S. Pat. No. 5,075,981. As can be seen from the description of this apparatus, it deals with a variety of specific tasks.